Clouds and Fog

Question 1

Definition of a cloud

Answer 1

Cloud

An aggregate of tiny moisture droplets and ice crystals; classified by altitude of occurrence and shape.

Question 2

What is fog?

Answer 2

Fog, discussed later in the chapter, is simply a cloud in contact with the ground.

Question 3

What is a Moisture Droplet?

Answer 3

Moisture droplet
A tiny water particle that constitutes the initial composition of clouds. Each droplet measures approximately 0.002 cm (approximately 20 μm (micrometers)) in diameter and is invisible to the unaided eye.

Question 4

What are Cloud-condensation nuclei ?

Answer 4

Cloud-condensation nuclei
Microscopic particles necessary as matter on which water vapour condenses to form moisture droplets; can be sea salts, dust, soot, or ash

Question 5

How are clouds formed?

Answer 5

As an air parcel rises, it may cool to the dew-point temperature and 100% relative humidity. (Under certain conditions, condensation may occur at slightly less or more than 100% relative humidity.) More lifting of the air parcel cools it further, producing condensation of water vapour into water.

Question 6

What are the two processes that account for the majority of the worlds raindrops and snowflakes?

Answer 6

Two principal processes account for the majority of the world’s raindrops and snowflakes: the collision–coalescence process, involving warmer clouds and falling coalescing droplets, and the Bergeron ice-crystal process, in which supercooled water droplets evaporate and are absorbed by ice crystals that grow in mass and fall.

Question 7

What are the 3 types of low clouds, how high up and what are they composed of?

Answer 7

Low clouds (CL)

Up to 2000 m, Water

Stratus (St) - Uniform, featureless, grey clouds that look like high fog.

Stratocumulus (Sc) - Soft, grey, globular cloud masses in lines, groups, or waves.

Nimbostratus (Ns) - Grey, dark, low clouds with drizzling rain.

Question 8

What are the two types of middle clouds, how high and what are they composed of?

Answer 8

Middle clouds (CM)

2000–6000 m, Ice and water

Altostratus (As) - Thin to thick clouds, with no halos. Sun’s outline just visible through clouds on a grey day.

Altocumulus (Ac) - Clouds like patches of cotton balls, dappled, and arranged in lines or groups

Question 9

What are the three kinds of high clouds, where do they occure and what are they made of?

Answer 9

High clouds (CH)

6000–13 000 m, Ice

Cirrus (Ci) - “Mares’ tails” clouds—wispy, feathery, with delicate fibres, streaks, or plumes.

Cirrostratus (Cs)- Clouds like veils, formed from fused sheets of ice crystals, having a milky look, with Sun and Moon halos.

Cirrocumulus (Cc) -Dappled clouds in small white flakes or tufts. Occur in lines or groups, sometimes in ripples, forming a “mackerel sky.”

Question 10

What are the two kinds of vertically developed clouds, where do they occur and what are they composed of.

Answer 10

Vertically developed clouds

Near surface to 13 000 m

Water below, ice above

Cumulus (Cu)- Sharply outlined, puffy, billowy, flat-based clouds with swelling tops. Associated with fair weather.

Cumulonimbus (Cb) - Dense, heavy, massive clouds associated with dark thunderstorms, hard showers, and great vertical development, with towering, cirrus-topped plume blown into anvil-shaped head.

Question 11

What two factors are key to cloud classification?

Answer 11

Altitude and shape are key to cloud classification.

Question 12

What are the three basic forms that clouds occur in?

Answer 12

Clouds occur in three basic forms—flat, puffy, and wispy

Question 13

How are flat and layered clouds classed?

Answer 13

Flat and layered clouds with horizontal development are classed as stratiform.

Question 14

How are puffy and globular clouds classed?

Answer 14

Puffy and globular clouds with vertical development are cumuliform.

Question 15

How are wispy clouds high in altitude and made of ice crystals classed?

Answer 15

Wispy clouds, usually quite high in altitude and made of ice crystals, are cirroform.

Question 16

What are Cumulus clouds?

Answer 16

Bright and puffy cumuliform clouds up to 2000 m in altitude.

Cumulus clouds appear bright and puffy, like cotton balls. When they do not cover the sky, they float by in infinitely varied shapes.

Question 17

What are Stratus clouds?

Answer 17

Stratus 
A stratiform (flat, horizontal) cloud generally below 2000 m. When they yield precipitation, they become nimbostratus

Question 18

What are Nimbostratus clouds?

Answer 18

Nimbostratus

Rain-producing, dark, greyish stratiform clouds characterized by gentle drizzle

Question 19

What are Stratocumulus clouds?

Answer 19

Stratocumulus

A lumpy, greyish, low-level cloud, patchy with sky visible, sometimes present at the end of the day

Question 20

What are altocumulus clouds?

Answer 20

Altocumulus (7)
Middle-level, puffy clouds that occur in several forms: patchy rows, wave patterns, a “mackerel sky,” or lens-shaped “lenticular” clouds.

The prefix alto- (meaning “high”) denotes middle-level clouds. They are made of water droplets, mixed, when temperatures are cold enough, with ice crystals. Altocumulus clouds, in particular, represent a broad category that includes many different styles: patchy rows, wave patterns, a “mackerel sky,” or lens-shaped (lenticular) clouds.

Question 21

What are Cirrus clouds?

Answer 21

Cirrus (7)
Wispy, filamentous ice-crystal clouds that occur above 6000 m and appear in a variety of forms, from feathery hairlike fibres to veils of fused sheets

Ice crystals in thin concentrations compose clouds occurring above 6000 m. These wispy filaments, usually white except when coloured by sunrise or sunset, are cirrus clouds (Latin for “curl of hair”), sometimes dubbed “mares’ tails.”

Question 22

What is a Cumulonimbus cloud?

Answer 22

Cumulonimbus (7)
A towering, precipitation-producing cumulus cloud that is vertically developed across altitudes associated with other clouds; frequently associated with lightning and thunder and thus sometimes called a thunderhead.

A cumulus cloud can develop into a towering giant called cumulonimbus (again, nimbus in Latin denotes “rain storm” or “thundercloud”; Figure 7.18). Such clouds are known as thunderheads because of their shape and associated lightning and thunder.

Question 23

What dose the presence of fog tell us?

Answer 23

The presence of fog tells us that the air temperature and the dew-point temperature at ground level are nearly identical, indicating saturated conditions.

Question 24

What generally caps a fog layer?

Answer 24

A temperature-inversion layer generally caps a fog layer (warmer temperatures above and cooler temperatures below the inversion altitude), with as much as 22 C° difference in air temperature between the cooler ground under the fog and the warmer, sunny skies above.

Question 25

What is Radiation fog?

Answer 25

Radiation fog (7)
Formed by radiative cooling of a land surface, especially on clear nights in areas of moist ground; occurs when the air layer directly above the surface is chilled to the dew-point temperature, thereby producing saturated conditions.

Question 26

What is rime fog?

Answer 26

Rime fog

A fog that consists of supercooled water droplets that turn into rime frost on contact with freezing objects.

Question 27

What are the five different kinds of fog?

Answer 27

Radiation, Rime, Ice-crystal, Advection, Evaporation.

Question 28

What is Ice-crystal fog?

Answer 28

Ice-crystal fog (7)
A type of fog that develops at very low temperatures in a continental arctic air mass. Visibility is seriously limited when the air becomes full of ice crystals that have formed by sublimation.

Question 29

What is Advection fog?

Answer 29

Advection fog (7)
Active condensation formed when warm, moist air moves laterally over cooler water or land surfaces, causing the lower layers of the air to be chilled to the dew-point temperature

Question 30

What is Upslope fog?

Answer 30

Upslope fog (7)
Type of advection fog.
Forms when moist air is forced to higher elevations along a hill or mountain and is thus cooled.

Question 31

What is valley fog?

Answer 31

Valley fog (7)
Type of advection fog
The settling of cooler, more dense air in low-lying areas; produces saturated conditions and fog. (Compare Upslope fog.)

Question 32

What is evaporation fog?

Answer 32

Evaporation fog (7)
A fog formed when cold air flows over the warm surface of a lake, ocean, or other body of water; forms as the water molecules evaporate from the water surface into the cold, overlying air; also known as steam fog or sea smoke.